Field of the Invention
The invention relates in general to a method for fabricating a light-emitting diode (LED) device, and more particularly to a method for the fabricating LED device, wherein the sacrificial dielectric layer is wet etched to remove a substrate.
Description of the Related Art
Light-emitting diode (LED) has a P/N junction and emits a light when a voltage is applied to the P/N junction. LED elements can be widely used in various fields, such as indicators, sign boards, illumination, and other illuminating elements. Due to the advantages of small sizes, long lifespan, low power consumption, and high luminosity, LED has gradually replaced conventional lamps and become a most important light-emitting element.
In general, the LED device may include a substrate, a buffer layer formed on the substrate, and an epitaxial light-emitting structure formed on the buffer layer. When emitting a light, the LED generates heat, and the light-emitting performance of the LED will deteriorate if the heat cannot be dissipated. The use of a thermally conductive substrate helps to dissipate the heat generated by the LED device. Some commonly used LED substrates, such as a sapphire substrate, despite being excellent epitaxy growth substrates, have low heat transfer coefficients and cannot produce satisfactory thermal transfer effects. A commonly used method for resolving the above problem includes: removing the substrate by a laser lift-off process; and then bonding a part of the LED removed from the substrate to a thermally conductive substrate. A vertical type GaN LED device is taken for example. Firstly, an undoped GaN layer is grown on a sapphire substrate. Next, an n-type GaN layer, a multiple quantum well, a p-type GaN layer, and a metal layer are sequentially formed on the undoped GaN layer, wherein the position of the n-type GaN layer and the position of the p-type GaN layer are exchangeable. Then, the sapphire substrate is removed by laser lift-off technology, and the above-mentioned structure having the undoped GaN layer, the n-type GaN layer, the multiple quantum well, the p-type GaN layer, and the metal layer is bonded to a metal substrate such as a copper substrate via a metal layer. Thus, the LED device has a thermally conductive metal substrate. However, the method for fabricating a LED device by using a laser lift-off process results in a poor yield, and the yield is even worse for large-size substrates (such as ≧3″). Therefore, a substrate removal process which produces better yields than the conventional laser lift-off process does is needed to replace the conventional laser lift-off process.